Jeffrey McCormick, a 37-year-old salesman, has a history of diabetes mellitus and moderate obesity. During his annual physical exam, the physician orders various blood and urine tests. When reviewing test results the next day, you note that Mr. McCormick’s blood glucose and urine microalbumin (MA) levels are high.
Should you be concerned? If you’re hesitating to answer, this article will help you understand the significance of the urine MA test.
Overview
The urine MA test analyzes urinary levels of albumin, a protein produced by the liver. Although albumin appears in high concentrations in the blood, normally it doesn’t spill into the urine.
However, in renal disease, the renal tubules become less effective at filtering the blood and reabsorbing proteins. Tiny amounts of albumin then leak into the urine—a condition called microalbuminuria.
Rationale for test
The urine MA test screens for early renal failure in patients with diabetes, hypertension, and certain other chronic conditions. It can identify renal disease several years before it becomes significant enough to cause symptoms. In diabetics, the test can detect diabetic nephropathy 5 years earlier than urine protein tests. Early recognition of developing renal failure enables clinicians to order measures that help prevent or minimize renal complications of these conditions. For Mr. McCormick and other diabetics with elevated urine MA levels, physicians typically recommend calorie restrictions, weight loss, and increased exercise to lower the urine MA level and decrease the risk (or slow the progress) of renal failure. In critically ill patients, physicians may order urine MA testing to predict outcome.
Who should be tested
• The National Kidney Foundation recommends annual urine MA screening for type 2 diabetic patients younger than age 70 and for type 1 diabetic patients older than age 12.
• The American Diabetes Association recommends annual urine MA testing for type 2 diabetic patients. For type 1 diabetics, it recommends annual testing starting 5 years after diabetes is first diagnosed.
• Some clinicians may order MA testing when a patient is first diagnosed with type 2 diabetes.
Test procedure
For mass urine MA screening, using a urine test strip on a random (spot) fresh urine specimen is the least expensive method. To perform this qualitative test, dip a urine test strip into the urine; then read the strip at the time indicated on the kit instructions and compare it to a color scale. If the test is positive, repeat it twice; if two of the three tests are positive, perform a quantitative measurement, using either a random or a 24-hour urine specimen. In this quantitative test, the urine MA level is measured and reported in mg/L or mg/day. The 24-hour test yields the most accurate measurement. However, it’s cumbersome and relies on patient compliance. Some patients may use home collection kits for mail-in testing. The laboratory may mail, fax, or e-mail test results directly to the patient or may post them on a confidential website.
MA/creatinine ratio. Measuring urinary creatinine (an indicator of urine concentration) in conjunction with the random MA test yields the MA/creatinine ratio. This ratio is important because hydration status can affect MA levels. The test estimates the amount of urinary albumin and corrects for differences in urine concentration. The MA/creatinine ratio approaches the accuracy of the 24-hour test while avoiding the need to collect a 24-hour urine specimen.
Normal values
• Urine MA: below 20 mg/L, or below 30 mg/day
• MA/creatinine ratio: less than 30 mg/g
Implications of abnormal values
• Moderately increased urine MA levels signify an early stage of chronic renal disease related to diabetes, nephropathy, or hypertension. Increased levels also may occur in patients with atherosclerosis, lipid abnormalities, myocardial infarction, myoglobinuria, hemoglobinuria, and Bence-Jones proteinuria.
• Very high urine MA levels suggest severe renal disease.
• MA/creatinine ratios above 30 mg/g indicate microalbuminuria.
Patients with consistently detectable urine MA are at increased risk for developing progressive renal failure and cardiovascular disease. In diabetics, the urine MA level relates to disease duration and glycemic control. Diabetics with elevated urine MA levels have a five- to tenfold increase in cardiovascular mortality, retinopathy, and end-stage renal disease.
Microalbuminuria also may be associated with nondiabetic nephropathies. In nondiabetic patients, urine MA elevation is an early sign of reduced life expectancy related to cardiovascular disease and hypertension.
Interfering factors
Urinary tract infections, blood in the urine, acid-base abnormalities, dehydration, and certain drugs (such as oxytetracycline) can elevate urine MA levels and falsely indicate a more serious prognosis. Vigorous exercise or febrile illnesses may cause MA to appear in the urine temporarily.
Selected references
MacIsaac RJ, Jerums, G, Cooper, ME: New insights into the significance of microalbuminuria. Curr Opin Nephrol Hypertens. 2004;13:83-91.
Pagana K, Pagana T. Mosby’s Diagnostic and Laboratory Test Reference. 7th ed. St. Louis: Mosby/Elsevier; 2005.
Pagana K, Pagana T. Mosby’s Manual of Diagnostic and Laboratory Tests. 3rd ed. St. Louis: Mosby/Elsevier; 2006.
Tsioufis C, Dimitriadis K, Antoniadis, D, et al. Inter-relationships of microalbuminuria with the other surrogates of the atherosclerotic cardiovascular disease in hypertensive subjects, Am J Hypertens. 2004;17:470-476.
Kathleen D. Pagana, RN, PhD, is Professor Emeritus at Lycoming College in Williamsport, Pa., and President of Pagana Seminars & Presentations. She is the coauthor of 17 books on diagnostic and laboratory testing, including Mosby’s Diagnostic and Laboratory Test Reference and Mosby’s Manual of Diagnostic and Laboratory Tests. Ms. Pagana’s website is www.kathleenpagana.com.
